Preamplifier, and waveform shaping circuit incorporating same

Abstract

A preamplifier providing adequate boost even to weak and small input currents, and thus achieving favorable gain and signal-to-noise ratio. An input current is converted to a voltage, which is provided to a differential amplification section. A phase-adjusted version of that voltage signal also is provided to the differential amplifier, the differential amplifier thus outputting an amplified signal based on the phase difference between its inputs. The preamplifier may be incorporated on a single chip, using MOS transistors or gallium arsenide techniques. A level clamping device may be provided in the event that the input current exceeds a predetermined value. The inventive preamplifier also may be incorporated advantageously into a waveform shaping circuit.

What is claimed is: 
     
       1. A preamplifier comprising: a first current-voltage conversion circuit for converting an input current to a first voltage, and providing said first voltage accordingly;   a second current-voltage conversion circuit for converting said input current to a second voltage, and providing a second voltage accordingly;   a first phase adjusting circuit, responsive to said first voltage, for generating a first voltage signal having a first desired difference in phase in relation to said input signal;   a second phase adjusting circuit, responsive to said second voltage, for generating a second voltage signal having a second desired difference in phase in relation to the first voltage signal, said second desired difference being different from said first desired difference; and   a differential amplifier having a first input terminal receiving said first voltage signal and a second input terminal receiving said second voltage signal, said differential amplifier producing first and second output signals, having opposite phases, corresponding to a difference between said first and second voltage signals.   
     
     
       2. A preamplifier according to claim 1, further comprising: first voltage clamping means, connected to said first current-voltage conversion circuit, for clamping a level of said first voltage output by said first current-voltage conversion circuit when said input current exceeds a predetermined level; and   second voltage clamping means, connected to said second current-voltage conversion circuit, for clamping a level of said second voltage output by said second current-voltage conversion circuit when said input current exceeds said predetermined level.   
     
     
       3. A preamplifier comprising: a current amplifying circuit for amplifying an input current;   a current-voltage conversion circuit for converting said amplified current to a voltage;   a voltage clamping circuit, connected to said current-voltage conversion circuit, for clamping said voltage output by said current-voltage conversion circuit when said input current exceeds a predetermined level;   a first phase adjusting circuit, receiving an output of said voltage clamping circuit, for generating a first voltage signal having a first desired difference in phase in relation to said input signal;   a second phase adjusting circuit, receiving an output of said first phase adjusting circuit, for generating a second voltage signal having a second desired difference in phase in relation to the first voltage signal, said second desired difference being different from said first desired difference; and   a differential amplifier having a first input terminal receiving said first voltage signal and a second input terminal receiving said second voltage signal, said differential amplifier producing output signals corresponding to a difference between said first and second voltage signals.   
     
     
       4. A preamplifier comprising: a signal conversion circuit for converting an input current into a voltage signal, said signal conversion circuit comprising means for reducing a change in level of said voltage signal when said input current exceeds a predetermined value;   a phase adjusting circuit for adjusting a phase of said voltage signal and producing a phase-adjusted voltage signal; and   a differential amplifier, having a first input terminal receiving said voltage signal and a second input terminal receiving said phase-adjusted voltage signal, for producing first and second output signals corresponding to a difference in voltage between said voltage signal and said phase-adjusted voltage signal.   
     
     
       5. A preamplifier according to claim 4, further comprising means for dividing said input current into first and second divided currents, wherein said signal conversion circuit comprises first and second conversion means, each receiving a respective one of said first and second divided currents and converting said respective one of said first and second divided currents into respective first and second voltage signals; and wherein said phase adjusting circuit adjusts a phase of one of said first and second voltage signals.   
     
     
       6. A preamplifier according to claim 4, wherein said signal conversion circuit comprises: current amplification means for amplifying said input current; and   a pair of series-connected resistors, connected to said current amplification means, for converting said input current into said voltage signal; and   wherein said means for reducing a change of level of said voltage signal comprises a diode connected between one end of said series-connected resistors and a junction between said first and second series-connected resistors.   
     
     
       7. A preamplifier according to claim 5, wherein each of said first and second conversion means comprises: current amplification means for amplifying a respective one of said first and second divided currents;   voltage conversion means for converting a respective one of said amplified first and second divided currents to a voltage;   voltage clamping means, connected to said voltage conversion means, for clamping a level of a respective one of said first and second voltage signals when said input current exceeds said predetermined value; and   level shifting means, responsive to a respective one of said first and second voltage signals, for applying a bias to a respective one of said first and second voltage signals.   
     
     
       8. A preamplifier according to claim 5, wherein each of said first and second conversion means comprises respective first and second pluralities of MOS transistors, connected in a source follower configuration; said differential amplifier comprises another plurality of MOS transistors; and   wherein said preamplifier further comprises an additional MOS transistor, receiving a reset signal at a gate thereof, for switching said preamplifier between set and reset states.   
     
     
       9. A preamplifier according to claim 4, further comprising an internal voltage source, connected to said phase adjusting circuit, for decreasing a response time of said preamplifier. 
     
     
       10. A preamplifier comprising: a first signal processing system for amplifying an input signal to a desired level and producing an amplified output signal;   a second signal processing system for producing an output signal having a desired phase difference in relation to the amplified output signal from said first signal processing system;   a plurality of amplifiers, having different gains, for generating an output signal in correspondence to a voltage difference between the amplified output signal from said first signal processing system and the output signal from said second signal processing system; and   one of transmission selecting means for selectively transmitting one of the amplified output signal from said first signal processing system and the output signal from said second signal processing system to said plurality of amplifiers; and amplifier selecting means for selectively driving at least a desired one of said plurality of amplifiers.   
     
     
       11. A preamplifier according to claim 10, wherein said transmission selecting means comprises a switching circuit for selecting one of the amplified output signal from the first signal processing system and the output signal from the second signal processing system to obtain a selected output signal, and for transmitting the selected output signal to a selected one of said plurality of amplifiers. 
     
     
       12. A preamplifier according to claim 10, wherein said amplifier selecting means comprises a control circuit having at least one control signal input, for selectively feeding and cutting off power to said plurality of amplifiers. 
     
     
       13. A preamplifier according to claim 10, wherein said transmission selecting means comprises a switching circuit receiving both of said amplified output signal and said output signal from said second signal processing system, and transmitting said amplified output signal and said output signal to a selected one of said plurality of amplifiers. 
     
     
       14. A preamplifier according to claim 12, wherein said plurality of amplifiers comprises two amplifiers, and wherein said control circuit has one control signal input for selectively feeding and cutting off power to said two amplifiers. 
     
     
       15. A preamplifier according to claim 12, wherein said plurality of amplifiers comprises four amplifiers, and wherein said control circuit has two control signal inputs for selectively feeding and cutting off power to said four amplifiers. 
     
     
       16. A preamplifier comprising: a first signal processing system for amplifying an input signal to a desired level and producing an amplified output signal:   transmission means, having at least one input and a plurality of outputs, said transmission means receiving said amplified output signal and providing said amplified output signal selectively to one of said outputs:   a plurality of phase adjusting means, each connected to a respective one of said plurality of outputs of said transmission means, for adjusting a phase of said amplified output signal and producing a phase-adjusted amplified output signal; and   a plurality of amplifiers, each receiving said amplified output signal, and also receiving said phase-adjusted amplified output signal from a respective one of said plurality of phase-adjusting means, each of said plurality of amplifiers having a different gain, and each of said plurality of amplifiers having two outputs for producing respective output signals having opposite phases.   
     
     
       17. A waveform shaping circuit, comprising: an analog signal processing system for obtaining a voltage output corresponding to an input current, said analog signal processing system including a preamplifying circuit; and   a digital signal processing system, provided in series with said analog signal processing system, for obtaining a digital signal based on said voltage output, said digital signal processing circuit including an analog-digital conversion circuit:   wherein said preamplifying circuit comprises a phase adjusting circuit for adjusting a phase of said voltage output, such that said preamplifying circuit outputs a first voltage signal and a second voltage signal that is phase-adjusted with respect to said first voltage signal;   said preamplifying circuit further comprising a differential amplifying circuit having first and second terminals receiving said first and second voltage signals, respectively; and   wherein said analog-digital conversion circuit comprises a level clamping circuit for clamping an amplitude of the digital signal output from said analog-digital conversion circuit when said input current exceeds a predetermined level.   
     
     
       18. A waveform shaping circuit according to claim 17, wherein said waveform shaping circuit further comprises a fluctuating amplifying circuit, having two inputs and two outputs, for amplifying an output of said differential amplifying circuit, and for compensating for fluctuations in temperature and in said input current. 
     
     
       19. A waveform shaping circuit according to claim 17, wherein said digital signal processing system further comprises a level conversion circuit, having an input and an output, for converting said voltage output from an ECL level to a TTL level, said level conversion circuit including a reference voltage generating circuit provided at said input of said level conversion circuit, said waveform shaping circuit further comprising a first current source acting as a first reference voltage source, a front stage of said level conversion circuit having a second current source, an input driving section of said level conversion circuit having a second reference voltage source, said first current source being identical to said second current source, said first reference voltage source being identical to said second reference voltage source. 
     
     
       20. A waveform shaping circuit comprising: an analog signal processing system for obtaining a voltage output corresponding to an input current, said analog signal processing system including a preamplifying circuit; and   a digital signal processing system, provided in series with said analog signal processing system, for obtaining a digital signal based on said voltage output, said digital signal processing circuit including an analog-digital conversion circuit;   wherein said preamplifying circuit comprises:   a first phase adjusting circuit, responsive to said input current, for generating a first voltage signal having a first desired difference in phase in relation to said input current;   a second phase adjusting circuit, responsive to said input current, for generating a second voltage signal having a second desired difference in phase in relation to the first voltage signal said first desired difference being different from said first desired difference; and   a differential amplifier having a first input terminal receiving said first voltage signal and a second input terminal receiving said second voltage signal, said differential amplifier producing output signals corresponding to a difference between said first and second voltage signals; and   wherein said analog-digital conversion circuit comprises a level clamping circuit for clamping an amplitude of the digital signal output from said analog-digital conversion circuit when said input current exceeds a predetermined level.   
     
     
       21. A waveform shaping circuit according to claim 20, wherein said preamplifying circuit further comprises: a current amplifying circuit for amplifying said input current;   a current-voltage conversion circuit for converting said amplified input current to a voltage;   a voltage clamping circuit, connected to said current-voltage conversion circuit, for clamping said voltage output by said current-voltage conversion circuit when said input current exceeds a predetermined level;   wherein said first phase adjusting circuit receives an output of said voltage clamping means, said second phase adjusting circuit being responsive to an output of said first phase adjusting circuit, said first and second voltage signals being provided to said differential amplifier accordingly.   
     
     
       22. A waveform shaping circuit comprising, an analog signal processing system for obtaining a voltage output corresponding to an input current, said analog signal processing system including a preamplifying circuit; and   a digital signal processing system, provided in series with said analog signal processing system, for obtaining a digital signal based on said voltage output, said digital signal processing circuit including an analog-digital conversion circuit;   wherein said preamplifying circuit comprises:   a signal conversion circuit for converting said input current into a voltage signal;   a phase adjusting circuit for adjusting a phase of said voltage signal and producing a phase-adjusted voltage signal; and   a differential amplifier, having a first input terminal receiving said voltage signal and a second input terminal receiving said phase-adjusted voltage signal, for producing output signals corresponding to a difference in voltage between said voltage signal and said phase-adjusted voltage signal; and   wherein said analog-digital conversion circuit comprises a level clamping circuit for clamping an amplitude of the digital signal output from said analog-digital conversion circuit when said input current exceeds a predetermined level.   
     
     
       23. A waveform shaping circuit according to claim 22, wherein said signal conversion circuit comprises means for reducing a change of level of said voltage signal when said input current exceeds a predetermined value. 
     
     
       24. A waveform shaping circuit according to claim 22, further comprising means for dividing said input current into first and second divided currents, wherein said signal conversion circuit comprises first and second conversion means, each receiving a respective one of said first and second divided currents and converting said respective one of said first and second divided currents into respective first and second voltage signals; and wherein said phase adjusting circuit adjusts a phase of one of said first and second voltage signals.   
     
     
       25. A waveform shaping circuit according to claim 23, wherein said signal conversion circuit further comprises: current amplification means for amplifying said input current: and   a pair of series-connected resistors, connected to said current amplification means, for converting said input current into said voltage signal; and   wherein said means for reducing a change of level of said voltage signal comprises a diode connected between one end of said series-connected resistors and a junction between said first and second series-connected resistors.   
     
     
       26. A waveform shaping circuit according to claim 24, wherein each of said first and second conversion means comprises: current amplification means for amplifying a respective one of said first and second divided currents;   voltage conversion means for converting a respective one of said amplified first and second divided currents to a voltage;   voltage clamping means connected to said voltage conversion means, for clamping a level of a respective one of said first and second voltage signals when said input current exceeds said predetermined value; and   level shifting means, responsive to a respective one of said first and second voltage signals, for applying a bias to a respective one of said first and second voltage signals.   
     
     
       27. A waveform shaping circuit according to claim 24, wherein each of said first and second conversion means comprises respective first and second pluralities of MOS transistors, connected in a source follower configuration; said differential amplifier comprises another plurality of MOS transistors; and   wherein said preamplifier further comprises an additional MOS transistor, receiving a reset signal at a gate thereof, for switching said preamplifier between set and reset states.   
     
     
       28. A waveform shaping circuit comprising: an analog signal processing system for obtaining a voltage output corresponding to an input current, said analog signal processing system including a preamplifying circuit; and   a digital signal processing system provided in series with said analog signal processing system, for obtaining a digital signal based on said voltage output, said digital signal processing circuit including an analog-digital conversion circuit;   wherein said analog-digital conversion circuit comprises a level clamping circuit for clamping an amplitude of the digital signal output from said analog-digital conversion circuit when said input current exceeds a predetermined level;   wherein said preamplifying circuit comprises:   a first signal processing system for amplifying said input current to a desired level and producing an amplified output signal;   a second signal processing system for producing an output signal having a desired phase difference in relation to the amplified output signal from said first signal processing system;   a plurality of amplifiers, having different gains, for generating an output signal in correspondence to a voltage difference between the amplified output signal from said first signal processing system and the output signal from said second signal processing system; and   one of transmission selecting means for selectively transmitting one of the amplified output signal from said first signal processing system and the output signal from said second signal processing system to said plurality of amplifiers; and amplifier selecting means for selectively driving at least a desired one of said plurality of amplifiers.